Transportation of liquefied natural gas



Dec. 1, 1964 P.c.KE1TH TRANSPORTATION 0F LIQUEFIED NATURAL GAS FiledAug. 22, 1961 .,f seb a2 o 74 fle z g CARGO EXPANSDN INVENTQR. PerclvcllC. Kelh United States Patent() 3,159,004 TRANSPGRTATIN F LIQUEFEDNATURAL GAS Percival C. Keith, Peapack, NJ., assiguor to HydrocarbonResearch, Inc., New York, NX., a corporation of New .Iersey Filed Aug.22, i961, Ser. No. 133,197 3 Claims. (Ci. 62-45) This invention relatesto the transportation of liquefied natural gas and similar normallygaseous materials which must be maintained at temperature levels belowabout 40 F. to permit handling at substantially atmospheric pressure. Itparticularly relates to improvements concerning ship storage whereby theliquefied material may be transported by water carrier.

The liquefaction and storage of natural gas at about 260 F. has beensuggested as economical for supplying gas in industrial areas wherefluctuating gas demands often exceed the capacity of availablefacilities. Where, however, the available gas is at remote geographicareas and shipment must be by water borne carrier, many new problemshave arisen. Not only is ship transportation relatively slow, thuscausing long periods of heat infiltration which tends to vaporize asubstantial part of the cargo, but also a ship has substantialturbulence which, in itself, further tends to vaporize the liquid. In aship, these vapors are an especially serious hazard for they areexplosive when mixed with air.

My invention relates primarily to the handling of liquefied natural gasand to the control of vaporization of the liqiud but as hereinafterpointed out, it is also applicable to the handling of other liquefiedgases such as propane, oxygen or nitrogen which arefsubject toliquefaction at temperatures in the range of 40 F. to as low as 424 F.and thus subject to objectionable vaporization resulting from ambientheat iniltration.

A principal object of my invention is toprovide a simpliiied liquidstorage unit for liquefied gases which unit is suitable for assembly ina ships hold and inrwhich structural stability is combined with safety`against hazardous gases to the end that liquids may be readily stored'and discharged.

The invention further contemplates storing of the lique- 4lied gases inthe sub-cooled state so that under the normal As a specilic feature ofthe invention, it is proposed to. sub-cool liquefied natural gas to a`temperaturerof about F. below the bubble point so that a container3,159,004 Patented Dec. 1, 1964 ICC FIG. 1 is a schematic centraltransverse vertical section taken through a marine vessel.

FIG. 2 is a horizontal cross-section taken substantially on the line 2 2of FIG. 1.

of liquid when shipped overseas during a customary pei' riod will onlybe heated to a bubble point which is approximately 260 F. thus avoidingthe production Vof any hazardous vapors and making it possible todispense with a re-liquefaction equipment on board the carrier.

` Further objects and advantages of the invention will appear from thefollowing description of a preferred form `drawing illustrative thereofand in which:

As shown in FIG. l, the vessel 10 which is represented as a marinevessel such as a ship or barge, but which might also be a land Vehiclebody, is shown to have a supporting bottom 12, sides 14 and a top deckor flooring 16. While the vessel as shown includes at least a holdencompassed by these walls and the customary bulkheads and extends thefull depth below decks, it will be understood that the vessel might beof a multiple deck type and the unit shown might be a typical insulatedhold.

Within the defined hold I provide one or more liquid cargo containers ortanks 20 which are preferably made of aluminum. While these tanks may beof a suitable shape, I prefer to use a series of cylindrical tanks incontact one with another as shown in FIG. 2 and conveniently Welded toeach other as by means of the stays 22, to become a rigid one piecenest. This assures a common movement of all tanks about a central pointand thus does not interfere with expansion or contraction.

The tanks 20, if cylindrical, are provided with dished or hemisphericaltop and bottom portions with bottom skirt portions 26 which rest onandare Vpermanently afiixed as by welds, not shown, to an aluminum lioorplate 28. This plate, in turn, is provided with a knob 30 which extendsinto a suitable cooperating slot in the ilooring 32.

vThis flooring which is usually of oak planking is suitably `mounted oninsulation such as balsa wood generally shown at 36 carried on thebottom 12 of the hull.

On the side walls of the hold, including the bulkheads, I prefer to useone or more layers of semi-permanent or bonded insulation 36a whichconsists of foam glass or cork or ,other pre-shaped insulation. Thislayer is mounted lnpermanent array as by the use of suitable lbinderswhich hold it against the hull wall. With its celf insulation 36h whichmay be of rockwool packed in bags of a suitable dimension. The bagsthemselves are preferably of impervious material and thus serve todecrease gas currents. Such secondary insulation is appropriately heldin place to'leave a space 37 between the wall insulation and the tankswhich space can be used for an access space to permit an inspection orrepair of the outside ofthe tanks 20.V Such a space also becomes animportant insulator of the very cold surfaces of the tanks 20. A furtherspace, designated 40 in FIG. 2, between adjacent cylindrical tanks isalso large enough for inspection and repair. With rectangular tanks,this internal space is unnecessary.

The hold is completed by an` insulated cover 42 which is supported byskirts 43 on theV upper portions of the tanks 20. The cover includes analuminum plate 44 covered as by the use of cork or rockwool insulation45.

3 tanks 2@ in a hold through a lill header 60 with a normally liquefiedgaseous material such as natural gas. This header 60 is connectedthrough line 62 to the bottom of one of the tanks of the nest and by theintermediate transfer lines 64- it is possible to fill all of theremaining tanks in the nest. The last tank in the vseries is providedwith a discharge line 65 which discharges into surge tank 66. When theliquid .in the surge tank reaches the desired level, all of the tanks inthe particular nest are full.

During irl-transit periods, l find it desirable to maintain acirculation of liquid through the tanks to prevent any substantialtemperature differences. plished by the use ofl pump 7@ which takessuction by line 65 from the surge tank 66 and through discharge line '72and ll line 62 can continuously circulate the liquid through the tanksand back through `outlet line 65 to the surge tank. Normally, a turnoverof liquid on a daily basis assures uniform temperature of the liquid.

Discharge of the liquid from the tanks is preferably by theruse of ahigh pressure gas source such as an inert gas, for example, nitrogen orthe'same type of gas in storage, for example, natural gas. This may beconnected through gas header 74 through gas line '76 to the v.top ofthesurge tank 66. This will impose a head on the liquid in surge tank 66which in turn will force the liquid out through line 65 into the lasttank of the nest thence through lill line 62 to liquidy header 60.

During the `return trip of a ship such as described, it has been founddesirable to provide for a recirculation of low temperature gases suchas methane or nitrogen or mixtures thereof to assure a uniform lowtemperature of the tanks. lThis is accomplished by the use of blower S2which takes suction from the upper part of surge tank 66 through lineSil and then discharges through line SS'and cooler 34 into header 6i).By the same piping 62, tanks 2li., and piping 65, the gases flow backto= the surge tank 66. The `cooler 84% may be nitrogen cooled.

This is accomt Ordinarily provision is made for possible expansion o-fthe'liquidin the cargo tanks 20. As the liquid expands into surge tank66y through line 65, the excess may be drawn olf through pipe 3S to theexpansion tank 2.1. Ios- Ysible vapors can be vented through line 9i)back to the surge tank 66. v

The transportation or storage of a normally liquefied gas at about itsbubble Vpoint is usually accomplished at atmospheric pressurenotwithstanding the constant vapor- In such a Wunit,

ization of gas due to heat` infiltration. especially with aninflammable-gas, there is always a gas discharge which must be burned as'fuel or reliqueed.

If, however, gas is stored under sub-cooled liquid con- Y ditions, thevapor pressureis of a low absolute valueand the holds, again with theadvantage that the actual surface exposed to the gas is extremely smallwhen the total horizontal surface is considered. f

As a result, l nd that the solubility of nitrogen in the liquid methanedoes not present a technical problem, and, in fact, on revaporization assoonV as the methane is heated to be vaporized for use, the nitrogen isdriven oli. It is thus possible to maintain the liquid methane at atemperature condition under which it exerts a vapor pressure less thanone atmosphere absolute without in fact having a vacuum present in thechamber.

The degree of sub-cooling can be adjusted to the desired extent butnormally a ship voyage of a week would tend to boil ofi about 1.5% ofthe contents of the tanks resulting from about a 4 F. temperature rise.I prefer, under such conditions, to .sub-cool the methane to about -270'F. which is about 12 F. below the bubbling temperature. This can beaccomplished by a iinal stage of liquefaction which can be by heatexchange with liquid nitrogen.

My invention is particularly advantageous for ocean going shipment dueto the long period involved and the l advantage of eliminating expensivere-refrigerationequipment. It is also possible, however, tot benefitfrom my invention in connection with stationary storage vessels wheresub-cooling can be accomplished with less energy consumption than `there-liquefaction can be accomplished.

The pressurizing of the nest of tanks Ztl. not only to discharge liquidbut for other purposes, can be Vaccomplished by the use of reenforcedtanksand connections. In accordance with the invention, however, Iprovide only a secondary containment generally shown as a clad shield orcover element 45. This is-necessary only on the outside tanks of thenest and maybe aseries of welded plates. n

Preferably I use a series of WeldY pads or plates 46 attached in thelshop to the tanks. These weld pads'serve notV .only to Vattach the cladcover element l bu-t also the external filler plate or web 47. As thepads 46 are Shop aixed,'the remaining welding of thecover elementl 4Sand lillerplate i7 can be accomplished in the'field without in any wayweakening the tank structure.

It will be apparent from the foregoing Vdisclosure that modificationsmay be made'to my invention and I thus desire a broad interpretation `ofmy invention within the scope and spirit of the disclosure herein and ofthe claims appended hereinafter.

l. In the method Vfor the safe storage of a highly volatile,low'boiling, liquied, combustible gas inplarge volumes at temperaturesbelow the boiling point wherein the gas is liquefied under substantiallyatmospheric conditions, the further steps of sub-cooling the liquid ytoa temperature substantially below the boiling point wherein nthe vaporpressure conditionV is less than one equipment thathas been usedheretofore to reduce the danger, or loss,`oriboth, resulting from heatimiltration to liquefied gases in ship or land storage.

In addition, I floatfonthev liquid a substantially impervious sheet 92made of a suitable material such as aluminum which nearly covers theexposed liquid. While 7 l small and not objectionable. Y

There is the further advantage that this gas'ftends to Yworkon allof theliquid'inall of the tanks, in all of vpartial pressure substantiallyVatmosphericl and thereby .prevent inflow of air from the surroundingatmosphere andavoidV the formation of a combustible mixture withtheliquelied gas. n l2; The method of storage ofa combustible gas asclaimed in claim l wherein'the combustible gas is substantially Vliquidmethane, the sub-coolingis to a temperature in the order of 270 F. andthe blanketing Ygas isl nitrogen;

.V3i The method of storage 0fV a combustible gas as claimed Vin claim 2including the further step of covering a majorV part of the'exposedsurface of the liquid methane with a substantially gas 'impervioussurface to ,re-

occlusion.

References Cited in the le of this patent UNITED STATES PATENTS De MotteMar. 3, 1936 Zuiver July 21, 1936 Willenborg Aug. 4, 1936 Whidden May 8,1951 McLaughlin June 10, 1952 Payne July 22, 1952 Brandon Sept. 21, 19546 Brandon Oct. 11, 1955 Iamsen Oct. 25, 1955 Brandon Ian. 31, 1956Beckwith Aug.'4, 1959 Murphy May 30, 1961 Wiedemann et a1. May 1, 1962Aronson July 24, 1962 OTHER REFERENCES Advances in Cryogenic Engineering(Timmerhaus),

1. IN THE METHOD FOR THE SAFE STORAGE OF A HIGHLY VOLATILE, LOW BOILING,LIQUIFIED, COMBUSTIBLE GAS IN LARGE VOLUMES AT TEMPERATURES BELOW THEBOILING POINT WHEREIN THE GAS IS LIQUEFIED UNDER SUBSTANTIALLYATMOSPHERIC CONDITIONS, THE FURTHER STEPS OF SUB-COOLING THE LIQUID TO ATEMPERATURE SUBSTANTIALLY BELOW THE BOILING POINT WHEREIN THE VAPORPRESSURE CONDITION IS LESS THAN ONE ATMOSPHERE ABSOLUTE, CONFINING THELIQUID IN AN INSULATED STORAGE CONTAINER, INTERCONNECTING THE STORAGECONTAINER WITH A TANK OF RELATIVELY SMALL HORIZONTAL SURFACE, APPLYINGAN INERT AND RELATIVELY LOW SOLUBILITY GAS TO THE SMALL HORIZONTALSURFACE WHEREBY THE INERT GAS GOES INTO PARTIAL SOLUTION IN THE LIQUIDTO THEREBY MAINTAIN A PARTIAL PRESSURE SUBSTANTIALLY ATMOSPHERIC ANDTHEREBY PREVENT INFLOW OF AIR FROM THE SURROUNDING ATMOSPHERE AND AVOIDTHE FORMATION OF A COMBUSTIBLE MIXTURE WITH THE LIQUEFIED GAS.